This invention relates to the multishafted, continuous mixing and kneading of plastifiable materials and, more particularly, to the plastification of such materials using mutually engaging worm elements which rotate in the same sense with a constant axial separation. In their direction of advance, the worm elements are in successive zones with different numbers of threads, with a zone having a smaller number of threads following a zone with a larger number of threads.
A machine for such mixing and kneading is disclosed in German Offenlegungsschrift No. 2,236,902. In this machine, a single-threaded zone with a trapezoidal profile follows a double-threaded zone with a self-cleaning profile. Because of the trapezoidal profile, the single-threaded zone cannot act in a self-cleaning fashion. The result is a machine with a forward zone where mixing essentially takes place, accompanied by considerable shear. In the following zone, with a smaller number of threads, large shear forces are avoided and a high pressure build-up is achieved to permit suitable extrusion.
Accordingly, it is an object of the invention to facilitate the continuous mixing of plastifiable materials. A related object is to facilitate the simultaneous mixing and kneading of such materials.
Another object of the invention is to eliminate the need for using a trapezoidal profile in a continuous mixing and kneading operation. A related object is to overcome the disadvantages associated with the use of trapezoidal profiles, particularly the inability to effectuate self-cleaning in the operation of such a profile.
Still another object of the invention is to increase the facility with which materials being processed can be supplemented by additives. A related object is to provide for the addition of additives in a way that achieves homogeneity of plastifiable materials and their additives.